btrfs: async_thread: Fix workqueue 'max_active' value when initializing

At initializing time, for threshold-able workqueue, it's max_active
of kernel workqueue should be 1 and grow if it hits threshold.

But due to the bad naming, there is both 'max_active' for kernel
workqueue and btrfs workqueue.
So wrong value is given at workqueue initialization.

This patch fixes it, and to avoid further misunderstanding, change the
member name of btrfs_workqueue to 'current_active' and 'limit_active'.

Also corresponding comment is added for readability.

Reported-by: Alex Lyakas <alex.btrfs@zadarastorage.com>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

2 files changed, 35 insertions, 24 deletions

diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index 1ce06c849a86..3e36e4adc4a3 100644
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -42,8 +42,14 @@ struct __btrfs_workqueue {
 
         /* Thresholding related variants */
         atomic_t pending;
-        int max_active;
-        int current_max;
+
+        /* Up limit of concurrency workers */
+        int limit_active;
+
+        /* Current number of concurrency workers */
+        int current_active;
+
+        /* Threshold to change current_active */
         int thresh;
         unsigned int count;
         spinlock_t thres_lock;
@@ -88,7 +94,7 @@ BTRFS_WORK_HELPER(scrubnc_helper);
 BTRFS_WORK_HELPER(scrubparity_helper);
 
 static struct __btrfs_workqueue *
-__btrfs_alloc_workqueue(const char *name, unsigned int flags, int max_active,
+__btrfs_alloc_workqueue(const char *name, unsigned int flags, int limit_active,
                          int thresh)
 {
         struct __btrfs_workqueue *ret = kzalloc(sizeof(*ret), GFP_NOFS);
@@ -96,26 +102,31 @@ __btrfs_alloc_workqueue(const char *name, unsigned int flags, int max_active,
         if (!ret)
                 return NULL;
 
-        ret->max_active = max_active;
+        ret->limit_active = limit_active;
         atomic_set(&ret->pending, 0);
         if (thresh == 0)
                 thresh = DFT_THRESHOLD;
         /* For low threshold, disabling threshold is a better choice */
         if (thresh < DFT_THRESHOLD) {
-                ret->current_max = max_active;
+                ret->current_active = limit_active;
                 ret->thresh = NO_THRESHOLD;
         } else {
-                ret->current_max = 1;
+                /*
+                 * For threshold-able wq, let its concurrency grow on demand.
+                 * Use minimal max_active at alloc time to reduce resource
+                 * usage.
+                 */
+                ret->current_active = 1;
                 ret->thresh = thresh;
         }
 
         if (flags & WQ_HIGHPRI)
                 ret->normal_wq = alloc_workqueue("%s-%s-high", flags,
-                                                 ret->max_active,
-                                                 "btrfs", name);
+                                                 ret->current_active, "btrfs",
+                                                 name);
         else
                 ret->normal_wq = alloc_workqueue("%s-%s", flags,
-                                                 ret->max_active, "btrfs",
+                                                 ret->current_active, "btrfs",
                                                  name);
         if (!ret->normal_wq) {
                 kfree(ret);
@@ -134,7 +145,7 @@ __btrfs_destroy_workqueue(struct __btrfs_workqueue *wq);
 
 struct btrfs_workqueue *btrfs_alloc_workqueue(const char *name,
                                               unsigned int flags,
-                                              int max_active,
+                                              int limit_active,
                                               int thresh)
 {
         struct btrfs_workqueue *ret = kzalloc(sizeof(*ret), GFP_NOFS);
@@ -143,14 +154,14 @@ struct btrfs_workqueue *btrfs_alloc_workqueue(const char *name,
                 return NULL;
 
         ret->normal = __btrfs_alloc_workqueue(name, flags & ~WQ_HIGHPRI,
-                                              max_active, thresh);
+                                              limit_active, thresh);
         if (!ret->normal) {
                 kfree(ret);
                 return NULL;
         }
 
         if (flags & WQ_HIGHPRI) {
-                ret->high = __btrfs_alloc_workqueue(name, flags, max_active,
+                ret->high = __btrfs_alloc_workqueue(name, flags, limit_active,
                                                     thresh);
                 if (!ret->high) {
                         __btrfs_destroy_workqueue(ret->normal);
@@ -180,7 +191,7 @@ static inline void thresh_queue_hook(struct __btrfs_workqueue *wq)
  */
 static inline void thresh_exec_hook(struct __btrfs_workqueue *wq)
 {
-        int new_max_active;
+        int new_current_active;
         long pending;
         int need_change = 0;
 
@@ -197,7 +208,7 @@ static inline void thresh_exec_hook(struct __btrfs_workqueue *wq)
         wq->count %= (wq->thresh / 4);
         if (!wq->count)
                 goto  out;
-        new_max_active = wq->current_max;
+        new_current_active = wq->current_active;
 
         /*
          * pending may be changed later, but it's OK since we really
@@ -205,19 +216,19 @@ static inline void thresh_exec_hook(struct __btrfs_workqueue *wq)
          */
         pending = atomic_read(&wq->pending);
         if (pending > wq->thresh)
-                new_max_active++;
+                new_current_active++;
         if (pending < wq->thresh / 2)
-                new_max_active--;
-        new_max_active = clamp_val(new_max_active, 1, wq->max_active);
-        if (new_max_active != wq->current_max)  {
+                new_current_active--;
+        new_current_active = clamp_val(new_current_active, 1, wq->limit_active);
+        if (new_current_active != wq->current_active)  {
                 need_change = 1;
-                wq->current_max = new_max_active;
+                wq->current_active = new_current_active;
         }
 out:
         spin_unlock(&wq->thres_lock);
 
         if (need_change) {
-                workqueue_set_max_active(wq->normal_wq, wq->current_max);
+                workqueue_set_max_active(wq->normal_wq, wq->current_active);
         }
 }
 
@@ -351,13 +362,13 @@ void btrfs_destroy_workqueue(struct btrfs_workqueue *wq)
         kfree(wq);
 }
 
-void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int max)
+void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int limit_active)
 {
         if (!wq)
                 return;
-        wq->normal->max_active = max;
+        wq->normal->limit_active = limit_active;
         if (wq->high)
-                wq->high->max_active = max;
+                wq->high->limit_active = limit_active;
 }
 
 void btrfs_set_work_high_priority(struct btrfs_work *work)
diff --git a/fs/btrfs/async-thread.h b/fs/btrfs/async-thread.h
index b0b093b6afec..ad4d0647d1a6 100644
--- a/fs/btrfs/async-thread.h
+++ b/fs/btrfs/async-thread.h
@@ -69,7 +69,7 @@ BTRFS_WORK_HELPER_PROTO(scrubparity_helper);
 
 struct btrfs_workqueue *btrfs_alloc_workqueue(const char *name,
                                               unsigned int flags,
-                                              int max_active,
+                                              int limit_active,
                                               int thresh);
 void btrfs_init_work(struct btrfs_work *work, btrfs_work_func_t helper,
                      btrfs_func_t func,